During operation of an internal combustion engine, a fraction of combustion gases can flow out of the combustion cylinder and into the crankcase of the engine. These gases are often called “blowby” gases. The blowby gases include a mixture of aerosols, oils, and air. If vented directly to the ambient, the blowby gases can potentially harm the environment and/or may be subject to government emissions regulations. Accordingly, the blowby gases are typically routed out of the crankcase via a crankcase ventilation system. The crankcase ventilation system may pass the blowby gases through a coalescer (i.e., a coalescing filter element) to remove a majority of the aerosols and oils contained in the blowby gases. The coalescer includes filter media. The filtered blowby gases are then either vented to the ambient (in open crankcase ventilation systems) or routed back to the air intake for the internal combustion engine for further combustion (in closed crankcase ventilation systems).
Some crankcase ventilation systems utilize rotating coalescers that increase the filter efficiency of the coalescing filter elements by rotating the filter media during filtering. In rotating filter cartridges, the contaminants (e.g., oil droplets suspended and transported by blowby gases) are separated inside the filter media of the filter cartridge through the particle capture mechanisms of inertial impaction, interception, diffusion, and gravitational forces onto the fibers. By rotating the filter media, inertial impaction and gravitational forces are enhanced by the additional centrifugal force. Additionally, the rotation of the filter cartridge can create a pumping effect, which reduces the pressure drop through the filtration system. Rotating filter cartridges may include fibrous filters as well as centrifugal separation devices. However, many rotating coalescers are configured for outside-in flow through the filter media for ease of integration into engine compartments and crankcases. However, outside-in flow rotating coalescers suffer from high pressure drops and reduced fractional efficiency compared to inside-out flow rotating coalescers.